a. Field of the Invention
The present invention relates to a non-contact type vane pump adapted to prevent the generation of heat due to direct contact between the outer edges of the rotatively driven vanes and the inner surface of the pump casing.
B. Field of the Prior Art.
A vane pump is generally known of the constant-volume type comprising a casing having a cylindrical inner surface, an eccentric rotor disposed in the casing, and vanes fitted in substantially radial slots in the rotor in which they are guided for advancing and retracting movement.
In addition, by the term "substantially radial slot" is meant a slot extending radially in such a manner as to pass through or deviate from the center of the rotor. In this type, the driving of the rotor causes the vanes to be outwardly extended in the slots and urged against the inner surface of the casing by the action of centrifugal force, thus creating a sealing action, or cooperating with separately installed extending springs to increase such sealing action. Thus there is an advantage that the construction of the vanes and the sealing means are very simple. Particularly, the radial slots in the rotor can be dimensioned so that they are sufficiently deep and provide for a snug fit for the vanes.
Therefore, there is no need to provide a special sealing mechanism in the slot portion. The type, however, has a serious disadvantage that as the rotative speed of the rotor is increased, the wear of and the generation of heat in the vanes and the casing are increased since the vanes are pressed against the inner surface of the casing.